This invention relates to mixing and aeration of liquids, and more particularly relates to a venturi aeration device.
In many instances it is desirable to circulate and aerate a fluid, such as water, to remove harmful chemicals as well as add oxygen to the water. An aeration device may be beneficially employed in stagnant or polluted bodies of water to promote oxygenation for marine life and to assist in the bio-decomposition of pollutants. Such aeration is an important factor in the purification of water and is used particularly for waste water treatment. The principal objects of aeration are to add gases or volatile substances to the water or remove them or carry out both objectives simultaneously. Aeration can also be utilized to keep biological solids in suspension for treatment purposes.
Aeration in addition to or aside from mixing purposes can function to add oxygen in natural or waste water treatment to promote biochemical and chemical processes as well as the addition of oxygen to ground waters to oxidize and dissolve iron and manganese. Aeration can also be used for the removal of carbon dioxide and reduction of corrosion and interference with lime soda softening, as well as for the removal of hydrogen sulfide, odor, tastes, and decrease metal corrosion and concrete and cement deterioration. This process can also improve the efficiency of chlorination and remove volatile oils, odor and taste-producing substances caused by algae and other micro-organisms.
There is a wide choice of equipment that can be used for effective aeration of fluids, and in particular waste water. These devices can be divided into common classes which include diffused aeration systems; submerged turbine aerators; high and low-speed surface aerators; dispersed aerators; gravity aerators and spray aerators. Diffused air was the earliest aeration system and continues to be used. Surface aerators and turbine aerators have markedly increased in use in recent years. Submerged turbine aerators have been used where relatively short detention times have been required.
Transfer of gas, and in particular oxygen, occurs in three phases. The first phase is the contact of the oxygen molecules with a liquid surface producing an equilibrium condition at the interface between two compounds. In the second phase, oxygen molecules pass through the film or interface by diffusion and in the third phase the oxygen is mixed in the liquid or water by diffusion and convection. Turbulence of the surface of the liquid increases the surface and is responsible for increasing oxygen transfer to the body of liquid. Thus, the goals of aerator design and use are to generate the largest practicable area of interface between a given liquid volume and air; then build up a thick interfacial film by breaking it down and having as long as possible exposure time while maintaining the highest possible driving force or concentration difference for absorption or desorption.
In a diffused aeration system the transfer of oxygen depends upon the bubble size with problems being experienced in breaking down the bubbles to their smallest component. Further, the diffused system is not particularly adaptable for use in deep bases. In addition, fine bubble diffusers are subject to plugging problems often requiring air filtration and, usually, properly designed long narrow basins, resulting in increased construction costs. The submerged turbine aerator, while more efficient below the surface than diffused air, needs very high horsepower due to the lower oxygen transfer efficiencies. The surface aerator has the highest oxygen transfer but requires a very large area for proper aeration.